This invention relates to chromatographic separation media and to suspension polymerization.
Chromatographic separation media in the form of continuous polymeric beds with pores large enough for hydrodynamic flow are disclosed in U.S. Pat. No. 5,645,717 (Hjertxc3xa9n et al., issued Jul. 8, 1997) and U.S. Pat. No. 5,647,979 (Liao et al., issued Jul. 15, 1997) and European Patent Application No. EP 0 852 334 A1 (Bio-Rad Laboratories, Inc., published Jul. 8, 1998). These beds are termed xe2x80x9ccontinuousxe2x80x9d since each bed is a monolithic solid core occupying the lumen of a column or capillary, spanning the entire cross section of the column or capillary. The core is porous, with pores approximately 3-5 micron in diameter, and therefore larger than those of media conventionally known as macroporous media, whose pores are approximately 0.1 micron in diameter. The bed is formed in place inside the column or capillary, and the pores extend through the bed to serve as channels large enough to permit hydrodynamic flow or fast diffusion through the pores themselves. The bed contains substantially no pores of the xe2x80x9cmacroporousxe2x80x9d size. Due to the presence of large pores and the absence of macropores, most if not all of the solute movement through the bed occurs as hydrodynamic flow or rapid diffusion, with essentially none of the slow diffusive transport that typically occurs through the smaller pores of macroporous media. This avoidance of slow diffusive transport reduces band broadening, while the high surface area of the large through-pores provides high resolution and separation capacity. The large size of the through-pores also permits a high throughput rate through the column.
The large-pore media described in the two U.S. patents and the European application referenced above are formed in the columns or capillaries themselves as monolithic structures. It has now been discovered that the beneficial qualities of these media can also be achieved in chromatographic beads, thereby combining the advantages of the large pores with the versatility of beads. Beads afford the user the ability to pack the separation column or capillary at the site of use and the ability of the user to select the geometry, size, and bead diameter, each serving as a further variable in determining the degree of and resolution in the chromatographic separation and in determining the flow rates through the column. Thus, in accordance with this invention, chromatographic beads are prepared by suspension polymerization with the same pore characteristics as the large-pore media of the two United States patents and the European patent application referenced above. The beads thus contain through-pores with diameters of approximately 0.5 micron or greater in diameter, preferably about 0.5 micron to about 2.0 microns, with substantially no pores of the macroporous size or smaller, i.e., substantially no pores as small as 0.1 micron in diameter or less.
This invention extends to beads that differ widely in chemical composition and function as separation media. Further descriptions of the qualities of these beads, the manner in which they are prepared, and their methods of use are described in the succeeding sections of this specification.